Melt spinning apparatus for forming a solid amorphous or fine grained product from transition metal-rare earth element-boron type materials, especially iron-neodymium-boron type materials have included a tundish with a filler end and an outlet. A nozzle is located in the outlet for forming a fine jet stream of molten material that is quenched on a spinning wheel located closely adjacent the outlet of the nozzle. Prior apparatus for forming such a fine jet steam has included a first induction heater for heating the tundish to maintain a charge of the rare earth element containing metal alloy in a molten state for flow through the nozzle. Additionally, the apparatus may also have a second induction heater which surrounds the nozzle to maintain the molten metal at a viscosity which will enable it to flow through the nozzle and against the periphery of the spinning quench wheel.
In the past, such nozzles have been provided with an inwardly diverging entrance opening that communicates with a large bore formed through the full length of the nozzle. The nozzle has a flat surface at its outlet with a central orifice for forming the jet stream. The flow rate of the jet stream onto the periphery of the quench wheel is a function of the height of the molten material in the tundish as well as the temperature and composition of the material; the nozzle geometry including the shape of the entrance opening and the length and diameter of the large bore; the diameter and length of the orifice at the end of the nozzle; and the distance between the periphery of the quench wheel and the outlet of the discharge orifice from the nozzle.
It was believed that such nozzles should include an inwardly divergent entrance for the smooth flow of molten material into an elongated nozzle passage. It was further believed that the elongated nozzle passage should have a relatively large bore from the entrance of the nozzle leading to an orifice formed in a flat end wall of the nozzle to form a fine jet stream from the orifice.
When the orifice of such nozzle was eroded by the hot molten material, the flow rate of the melt increased to the point that the stream could not be cooled fast enough to obtain a desired microstructure. The production casting run then had to be shut down in order to replace an eroded nozzle with a new nozzle having a properly sized orifice.
A crucial factor in the production of good quality quenched solid product suitable for use in the manufacture of permanent magnet materials from the molten rare earth-containing material is that the outlet orifice diameter remain sufficiently close to its original size such that the melt stream can be suitably quenched by the spinning wheel.
Such prior art nozzles have used resistant refractory materials, such as boron nitride. Nevertheless, molten iron-neodymium-boron material eroded the orifice and the flow rate increased to the point that the material could no longer be quenched to a suitable amorphous or fine grained microstructure.
In order to improve the performance of nozzles, a series of experiments was undertaken to determine if the nozzle geometry could be varied so as to materially increase the duration of a casting run before nozzle wear at the outlet orifice required replacement of the nozzle. The experiments used a nozzle having the same stock material of boron nitride, the same tundish, the same induction heater, the same quench wheel and with only the geometry of the nozzle adjusted to determine if changes could be made to produce such material increases in the duration of casting runs.